Current terminal assemblies for making electrical connections to the motor component of a hermetic motor compressor unit include a plurality of conductor pins projecting through spaced apertures in a metal body member and hermetically sealed thereto are glass-to-metal seals. These terminal assemblies, as described for example in U.S. Pat. No. 3,160,460-Wycenbeek, include a cup-shaped metallic body member adapted to be inserted in an opening in a hermetic casing with the open end facing the interior of the casing and the side walls hermetically attached to the casing as by resistance welding. During operation of a hermetic compressor unit as part of the refrigeration system, metallic particles in a system are attracted to the surface of the glass insulator beads forming the glass-to-metal seals by a phenomenon known as electrophoresis and these particles form buildup on the surface of the glass to the point that an electrical conductive path is established resulting in a short circuit causing a terminal failure. Further contaminants within the system, such as moisture and acidic components such as halogen acids resulting from a partial decomposition of the halogenated hydrocarbon refrigerant, may also directly attack the glass surfaces causing or contributing to the electrical breakdown. Other causes of electrical breakdown of the terminal assembly is in the event of compressor motor failure. In this instance a carbon mixture often deposits on the inside of the hermetic terminal forming a conductive path between the terminal pins and ground. The carbon is generated by the high temperatures resulting during motor failure.
This problem may in part be aggravated in that presently available terminal assemblies include a generally cup-shaped body member with the recess portion facing the motor compressor unit. While the side walls of the cup-shaped terminal provide a convenient means of securing the assembly to the compressor case it should be noted that contaminants may collect and accumulate in the recess area.
For the purpose of preventing failure of terminals through integration of the glass U.S. Pat. No. 3,551,191-Elbling et al proposes coating at least the glass beads or bushing portions of the terminal with an impervious coating of an expoxy resin. While such a coating does protect the glass surfaces and prevent deterioration thereof by acidic disintegration, it does not materially decrease the potential tracking distance between terminals or prevent metallic particles from being attracted to the vicinity of the terminals with the formation of short circuiting electrically conductive paths. Another attempt at preventing failures of the terminal through disintegration of the glass is disclosed in U.S. Pat. No. 3,721,948-Brandt et al, assigned to the General Electric Company, the assignee of the present invention. Means are provided by this patent to substantially increase the over-surface distance between the terminal and the terminal grounds. This included providing sleeves of insulating material which surrounded each of the terminals in spaced relationship. While this attempt did in fact increase the over-all surface distance between the terminals, it involves the use of several extra parts that must be especially made, and require added steps in the assembly of the terminal.
While prior art terminals may prevent motor failure during the life of the compressor motor by accommodating a normal amount of contaminants expected to be found in a hermetic refrigeration system they have been found lacking during major catastrophic motor failures that generally produce large quantities of carbon that in effect completely cover or coat the cup-shaped area and particularly the glass seal areas between the conductor pins and terminal body of the terminal assembly.
Since these failures would occur during extremely high temperatures found or experienced during motor failures in the neighborhood of 2,000.degree. F., it can easily be understood that a blown pin will permit the extremely hot high pressure refrigerant to escape violently from the hermetic compressor casing. This high temperature fluid escaping under pressure may present a potential source of danger that could cause considerable damage in certain circumstances.
Accordingly, by the present invention, means are provided in a terminal assembly that will prevent terminal blowout during extreme motor failure conditions by isolating the vulnerable recess area of the terminal assembly from the motor compressor unit area.